fLIGHT International, 14 January 1965 75
Firing dotes and active lifetimes of the three
joint US/UK scientific satellites (from paper
by 8/onstein of BAC at the symposium)
schematics. These specifications and drawings were reviewed on an
as-produced basis by the project management staff. At this point
in project development, weekly meetings were held by project
management to promote schedule compatibility of the subsystems.
These meetings, attended by experimenters, subsystem designers,
test engineers, contractor personnel and the staff, served as a clearing
house for all compatibility problems for the duration of the project.
Schedule compatibility was aided by use of a PERT chart, which
was up-dated during the course of the project to reflect any antici-
pated slip-time due to late procurement of critical subsystems.
The interconnection system problems are best resolved as early
. as possible by management and system-integration personnel
interviewing each subsystem designer and experimenter, advising
them of the spacecraft wiring reliability objectives, and assisting
them in the assignment of specific redundant leads and pin connec-
tions, complete with pin numbers. The desired redundancy of
interconnections between subsystems must be decided during
subsystem specification generation. The general philosophy for
the optimum redundancy throughout the cabling assembly was to
provide redundant wiring for all critical signal and power leads.
This resulted in approximately 70 per cent of the conductors in
Ariel 2 being redundant.
Test specifications were generated by members of a test and
evaluation division as soon as the subsystem specifications were
completed. The interface test parameters and limits were arrived
at by conferences between the subsystem designers, integration
engineers, test engineers and project management staff. Each
interface of all subsystems was investigated for source and terminal
impedance values to obtain compatibility with the test equipment
complex. Determination of the number of test points requiring
monitoring was made on a subsystem basis first, then screened as
to their priority to reduce the number of test leads in the spacecraft
interconnecting harness to provide the desired overall system
monitoring. From the compatibility point of view, the fewer test
leads in a spacecraft system the better, since any one could introduce
detrimental crosstalk. From a test philosophy point of view, the
greater number of monitoring points obtained the better. A
compromise between these two viewpoints was made.
While all of the subsystem suppliers were engaged in the detailed
design and fabrication of their prototype and flight hardware, the
integration groups designed and produced all of the necessary
ground support equipment. The mechanical group designed all the
jigs, fixtures, spacecraft handling dollies and shipping containers
simultaneously with their design of the overall structure. The
electronic group designed and produced the spacecraft control and
spacecraft performance analysis systems prior to integration.
Fabrication and Test of Structures and Subsystems The fabrication
of the Ariel 2 spacecraft was started as soon as the subsystem
specifications and drawings were completed. There were changes
and modifications to both the specifications and drawings as the
fabrications proceeded.
For structural test purposes, two units were fabricated. The first
was a dynamic test unit which simulated the weight, size and centre
of gravity of the spacecraft and had all attaching appendages
necessary for the dynamic separation and de-spin tests. The second
unit constructed was an engineering test unit which closely simulated
the detailed structure of the completed spacecraft. Dummy sub-
systems and experiments inside the spacecraft were used for weight
and centre-of-gravity simulation. The skins, frame appendages and
separation system were exact duplications of those to be used in the
actual spacecraft. This unit was employed for vibration testing.
Several minor modifications to the structure were necessary to
correct defects which appeared during tests of the engineering test
unit.
The prototype structural assembly and the interconnection har-
ness fabrication was started at Westinghouse following successful
testing of the dynamic test unit. Fabrication of the interconnection
cabling system for the prototype was almost completed when re-
ports were received of a tendency of cadmium surfaces to produce
fine whisker growths under vacuum exposure. As a result, it was
necessary to delay fabrication of flight model interconnection
systems for some weeks pending receipt of gold-plated connectors.
The prototype experiments and subsystems packages of Ariel 2
were fabricated simultaneously with the prototype structure and
interconnection system. Since these packages were derived from
three sources (Westinghouse, United Kingdom and the Goddard
Center), considerable scheduling difficulties arose when attempting
to dovetail their "ready date" with that of the prototype structure
for integration.
Subsystems tests for Ariel 2 consisted of two types, design
qualification or prototype-level tests and flight-acceptance-level
tests. Subsystems fabricated for the prototype spacecraft or
engineering test units fabricated for design approval were subjected
to higher test levels than those subsystems fabricated for the flight
spacecraft. To be concluded
Intended to provide high-energy, upper-stage propulsion for advanced
and post-Saturn launch vehicles, the Aerojet-General M-l liquid-
hydrogen rocket engine is designed to develop I.S million pounds' thrust.
Here an M-1 nozzle, 17ft in diameter, is compared for size with a two-man
Gemini spacecraft at the Aerojet plant in Sacramento, California